Imported Upstream version 3.6.0

Former-commit-id: da6be194a6b1221998fc28233f2503bd61dd9d14

mcs/class/System.IO.Compression/SharpCompress/Common/Zip/SeekableZipFilePart.cs

@@ -0,0 +1,45 @@
+using System.IO;
+using SharpCompress.Common.Zip.Headers;
+
+namespace SharpCompress.Common.Zip
+{
+    internal class SeekableZipFilePart : ZipFilePart
+    {
+        private bool isLocalHeaderLoaded;
+        private readonly SeekableZipHeaderFactory headerFactory;
+
+        internal SeekableZipFilePart(SeekableZipHeaderFactory headerFactory, DirectoryEntryHeader header, Stream stream)
+            : base(header, stream)
+        {
+            this.headerFactory = headerFactory;
+        }
+
+        internal override Stream GetCompressedStream()
+        {
+            if (!isLocalHeaderLoaded)
+            {
+                LoadLocalHeader();
+                isLocalHeaderLoaded = true;
+            }
+            return base.GetCompressedStream();
+        }
+
+        internal string Comment
+        {
+            get { return (Header as DirectoryEntryHeader).Comment; }
+        }
+
+        private void LoadLocalHeader()
+        {
+            bool hasData = Header.HasData;
+            Header = headerFactory.GetLocalHeader(BaseStream, Header as DirectoryEntryHeader);
+            Header.HasData = hasData;
+        }
+
+        protected override Stream CreateBaseStream()
+        {
+            BaseStream.Position = Header.DataStartPosition.Value;
+            return BaseStream;
+        }
+    }
+}